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Galvanic surface coating explained clearly!

Learn the basics here.

The DIN EN ISO 4012 standard summarizes the essential aspects of surface coating in connection with electroplating.

Because more varieties and properties of coatings were added over time, the standard was completely revised and updated in 2018.

Basically, there are three essential things to consider when selecting a coating:

• The surface structure
• The standardized designation
• The risk of hydrogen embrittlement

The coating structure:

The above diagram clearly shows the possible layer structures.
Depending on the requirements, these can range from a simple coating to a multi-layer structure with a conversion layer and a sealant.

What is the task of each layer?

• The metal coating protects the base metal from corrosion.
• The conversion layer (chromating or passivation) makes the corrosion protection last longer and also provides better adhesion for additional coatings.
• An additional sealant/top layer increases the corrosion protection and also provides other characteristics such as tightening torque, resistance, thermal load capacity, mechanical strength, appearance, color, electrical resistance, UV resistance, etc.
  The top layer can contain a lubricant if a special torque/preload force ratio is required.

The standardized designation for surfaces:

The name for the galvanic surface coating has been repeatedly changed over time. Unfortunately, the original simple designation system “A1A” was no longer adequate because of the wide range of requirements and options. The three digits are no longer sufficient to clearly describe the extensive number of surface components for the products.

Original designation in the key numbering system A:
A3L describes the coating metal, the coating thickness and the post-treatment with the gloss level.
Key numbering system B:
Fe/Zn8c 2C describes the base metal Fe, the coating metal Zn, the nominal coating thickness 8my, the chromate c, the chromate class 2 and the chromate type C.

–> You can already see here that the information values differ significantly.

The revised standard has discontinued the previous designation systems for new projects. In particular, the method according to the “A1A” designation system must not be used for new applications; this is only included in the standard for information purposes.

Overview of the new designation:

The individual surfaces and each layer must be separated with a slash.

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